1. Field of the Invention
This invention relates to the drilling and workover of wells penetrating subterranean reservoirs, and more particularly to the drilling of such reservoirs with foam drilling fluid containing a biodegradable foaming agent.
2. Description of the Prior Art
It has long been conventional practice in the drilling of bore holes penetrating subterranean reservoirs to circulate a drilling fluid down the drill pipe and back up the bore hole annulus for the removal of debris and drill cuttings from the bore hole. Drilling fluid also serves to prevent sloughing in the bore hole during the drilling operation. Recently, air and gas have replaced conventional drilling fluids in the drilling of some bore holes, and have proved particularly beneficial in reservoirs wherein dense conventional drilling fluid would be lost to the reservoir. Additionally, air and gas have also provided longer bit life and higher rates of penetration in the drilling of bore holes.
However, in many reservoirs, water enters the bore hole from adjacent water-containing strata; and air and gas have proved unable to remove this water. In view of this problem, foams have been developed to remove both the cuttings and the water from these bore holes. Numerous foam compositions have been proposed and used. A suitable foam should be stable enough to withstand the rigors of circulation through the bore hole without appreciable breaking into its component parts so as to assure adequate removal of cuttings from the bore hole. At the same time, environmental considerations require that the foaming agent in a foam circulated out of a well and stored at the earth's surface biodegrades within a reasonable period of time to aid in its disposal. Previously used foams have not been able to completely satisfy the dual requirements of adequate stability during circulation and biodegradability upon storage.
Accordingly, a principal object of this invention is to prove a method of conducting foam drilling and workover operations in subterranean reservoirs.
Another object of the invention is to provide such a method employing a biodegradable foaming agent.
A further object of the invention is to provide such a method wherein the foam which is circulated through the well bore and then stored, subsequently breaks into its component parts.
A still further object of the invention is to provide such a method employing a foaming agent which is both stable during use and biodegradable during subsequent storage as a constituent of a foam.
Other objects, advantages and features of the invention will become apparent to those skilled in the art from the following description.